Remote telemetry is a technique by which telemetry data collected at a remote location is collected in a central repository (e.g., a host computer) for analysis and archival purposes. The telemetry data might be any physical measurement, such as a liquid level, weight, pH, chlorine concentration, temperature, pressure, proximity, etc., and is sensed by a Remote Telemetry Unit (RTU). It is common for a number of RTUs to be in relatively close proximity to one another (e.g., on a factory floor); even though they might be quite a distance from the central host (e.g., in another city).
In many potential applications of remote telemetry, there are barriers that must be overcome to make the application feasible. One barrier present in many situations is the need to establish two-way communications between each RTU and the central host in a manner that is inexpensive and/or power efficient. Examples of such two-way links commonly include dedicated telephone lines, cellular telephone links, wireless data networks, shared media data networks, and other wireless technologies. Each of these two-way links has drawbacks. A high financial cost is associated with dedicated telephone lines due to regulations limiting the routing of the phone lines, as well as regulations controlling the cost to the consumer. Similar high costs are associated with cellular telephone networks and data networks, which must pay either a monthly fee or per packet of information transferred. In the case of wireless technologies, there must be a wireless receiver active at all times as to receive signals transmitted either from the RTUs or from the host computer.
U.S. Pat. No. 6,014,089 to Tracy et al. for “Method For Transmitting Data Using Digital Control Channel Of A Wireless Network,” herein incorporated by reference, discloses an apparatus and method for transmitting data to and from a data collection device using the short message service functionality of the control channel of a personal communications system transmission protocol. The '089 patent discloses a method wherein a request for data from a remote device is transmitted to a data collection device using the short message service portion of a digital personal communications system control channel protocol. The requests are received at the data collection device, interpreted, and the requested data compiled therein. The compiled data is then transmitted back to the remote device from the data collection device on the same short message service portion of the digital personal communications system control channel as was used to transmit the request for data.
U.S. Pat. No. 5,892,758 to Argyroudis for “Concentrated Subscriber Wireless Remote Telemetry System” and U.S. Pat. No. 5,748,104 to Argyoudis for “Wireless Remote Telemetry System”, both herein incorporated by reference, each disclose variations on a wireless remote telemetry system utilizing low-cost remote communications devices operating on an existing wireless communications system in order to provide real-time reading and control of the remote devices. In these systems, remote metering devices collect and forward data to an associated wireless remote telemetry device which in turn, relays data over existing wireless communications systems, such as cellular base stations, using a shared random access channel to a central controller. The central controller of these systems, in turn, regulates the operation of the wireless remote metering units by transmitting messages over a corresponding paging channel. The shared random access channel and the associated paging channel are separate logical partitions of a single physical mechanism for delivering data. Specifically, these patents disclose using a PCS communications link having a common frequency band and utilizing CDMA code to establish a link. Furthermore, to effectively utilize this system, each of the remote telemetry units is required to have a unique address on the two-way communications link, such that the central controller can communicate individually with each remote unit over this link.